The present invention relates to a coupling catalyst comprising a nickel compound and a nitrogen-containing cyclic compound and a process for producing a coupling compound by reacting an unsaturated organic compound and boron compound using the catalyst.
There has been a growing demand for biaryl type coupling compounds as production intermediates for producing pharmaceuticals, agrochemicals, liquid crystal material, and organic electronic luminescence material. Suzuki coupling reaction comprising reacting a boron compound with an aryl halide compound by using a nickel catalyst can be mentioned as a versatile process for producing biaryl type coupling compounds. In the reaction, phosphine compounds have been exclusively used as a ligand of the nickel catalyst, and a catalyst using an amine compound as the ligand in the reaction were only rarely known for a catalyst using 2,2′-bipyridyl or triethylamine since it has been well known in the art that an amine compound having a nitrogen atom, which is an element of Group 15 of the Periodic Table of Elements as the phosphrous atom of a phosphine, is inferior to phosphine ligand in their ability to coordinate with a metal atom (Yukigosei Kagaku Kyokaishi, vol. 58, August, 2000, p. 736–744, Tetrahedron Vol. 55, p. 1889,1993). The coupling reaction using 2,2′-bipyridyl or triethylamine were not always satisfactory in that the reaction using the catalyst containing 2,2′-bipyridyl ligand is accompanied by a significant amount of byproducts and reaction activity of the catalyst containing triethylamine was limited.
Nickel complexes prepared from a hydrate of nickel chloride, bromide or iodide or nickel nitrate, and 1-methylimidazole or 1,2-dimethylimidazole in a mixture of ethanol and 2,2-dimethoxypropane were known, however, catalytic activity of these compounds were not known nor suggested (Inorganic Chimica Acta., pp. 406–410 September, 1969).